Many subsea projects require the ability to safely and accurately lift heavy loads from the seabed. In many cases, the preferred option is to conduct this lifting on the seabed itself, rather than lifting from a surface vessel, since the seabed is stable and can support virtually unlimited loads. In many applications, the weight of the lifting appliance and its payload have to be spread across a large surface of the seabed using large, cumbersome structures known as “mud mats.”
Problems exist with simply installing two piles and laying a gantry “beam” across the top, e.g. it is nearly impossible to locate a second pile an exact distance from the first installed pile; it is nearly impossible to install either pile plumb; it is nearly impossible to raise and lower both piles synchronously; and the position of the lifting interface relative to the object to be lifted is nearly impossible to locate exactly when the piles are installed.